This invention relates generally to ultrasonic welding processes and more particularly to a method and device for picking and placing component parts for an ultrasonic welding process.
Ultrasonic welding joins parts by applying mechanical energy from a high frequency vibration source at a joint formed between two component parts. Generation of ultrasonic energy includes the conversion of high frequency electrical energy by an electromechanical converter or transducer to a mechanical vibration. Mechanical vibrations are amplified by an amplitude transformer and applied to a workpiece by means of an ultrasonic xe2x80x9chornxe2x80x9d. In order to effect the weld joint, a first component part is typically positioned in a fixture while a second component part is mechanically vibrated against the relatively stationary first component part. The mechanical vibration is produced at a frequency generally in the range of 20,000 (20 kHz) or 40,000 (40 kHz) cycles per second. The high frequency vibration is ordinarily accompanied by a compressive force generated by the horn between the mechanically vibrated second component part and the relatively stationary first component part. The ultrasonic welding process is capable of breaking down films and oxides creating a coalescence between the component parts at the site of the weld. A superior joint may be achieved without the use of filler materials, fluxes, adhesives, epoxies or mechanical connectors.
One challenge common in production settings, wherein ultrasonic welding processes are employed, relates to picking and placing of component parts to be welded. Commonly, during an ultrasonic welding process, a relatively stationary first component part is held in a fixture, xe2x80x9cnestxe2x80x9d or xe2x80x9canvilxe2x80x9d. The fixture is most often configured to support and conform at least generally to a configuration of the first component part. A second part to be attached by welding to the first part must be picked and placed in position relative to the first part prior to welding. According to the prior art, this has been accomplished by a separate apparatus commonly necessitating a distinct workstation and oftentimes an additional and attendant transport mechanism for transporting the second part, once it is picked, from a parts pickup station to a fitting station wherein the second part is placed in position for welding. The transport mechanism then transports the parts to a second position wherein the actual ultrasonic welding process takes place. In addition, this arrangement typically requires that either or both the first part and the second part be designed to provide a physical feature for trapping or temporarily holding the second piece in relationship to the first piece during transport to the welding station. Alternately, the first part may be temporarily attached to the second part by a separate and distinct process such as heat staking or xe2x80x9ctackingxe2x80x9d.
There may be advantage in providing an ultrasonic weld horn that includes the additional functionality of picking and placing a second part in position for welding.
The present invention is directed to a combination ultrasonic weld horn/vacuum pickup including an ultrasonic weld horn having a vacuum conduit. A vacuum or negative pressure is directed through the vacuum conduit providing necessary suction at the tip of the weld horn to permit the weld horn to pick and hold a first component part during positioning of the part for welding to a second component part. In the preferred embodiment of the invention, the conduit is formed as a bore milled along a longitudinal axis of the weld horn. The longitudinal bore is joined by a second aperture drilled or milled from the side wall of the weld horn and intersecting the longitudinal bore at a neutral point along the horn. The neutral point is a point located along the length of the weld horn that is subjected to a minimum of movement during the ultrasonic welding process. Location of the weld horn at the neutral point significantly reduces or otherwise eliminates breakage or failure of the horn or the fitting attaching the vacuum source to the weld horn due to stresses observed in the weld horn during the ultrasonic welding process. The diameter of the bore may vary depending upon the vacuum being applied through the conduit and the mass of the part being picked. The tip of the weld horn may be further adapted or configured to conform or otherwise accommodate the configuration of the part being picked. The combination ultrasonic weld horn/vacuum pickup provides both the functionality of picking a first part and placing the first part in relationship to a second part and ultrasonically welding the first part to the second part.
The present invention is directed to an ultrasonic welding system including a part supply station, a weld station, a combination ultrasonic weld horn/vacuum pickup and a transport mechanism for transporting the ultrasonic weld head between the part supply station and the weld station. The weld station includes a fixture for supporting a first component part. The part supply station includes a location where the first component part or a plurality of sequentially fed first component parts are positioned for pickup by the combination ultrasonic weld horn/vacuum pickup. The weld station may be configured as a turret or other automated production facility component for sequentially positioning a plurality of second component parts for fitting with and welding to the first component parts. The transport mechanism includes a combination ultrasonic weld horn/vacuum pickup support member, an X axis transport mechanism and a Z axis transport mechanism.
The present invention is also directed to a method for picking a first part and placing the first part in relationship to a second part in preparation for ultrasonically welding the first part to the second part. The method for joining two parts employing an ultrasonic welding process includes the steps of vacuum assist picking a first component part from a first component part supply station with a combination ultrasonic weld horn/vacuum pickup, positioning the combination ultrasonic weld horn/vacuum pickup and the first component part relative to the second component part in preparation for ultrasonically welding the first component part to the second component part and ultrasonically welding the first component part to the second component part with the combination ultrasonic weld horn/vacuum pickup.